The present invention is directed to a running tool for installing a tubular hanger in a subsea wellhead housing or the like. More particularly, the invention is directed to a running tool which may be used to land the tubular hanger in the wellhead housing, set an annulus seal assembly between the tubular hanger and the wellhead housing, and then pressure test the annulus seal assembly, all in a single trip and without the need for a riser or a blowout preventer.
In subsea oil and gas production systems, casing hangers are used to suspend corresponding casing strings from a wellhead housing or the like installed on the sea floor. After the casing hanger is landed in the wellhead housing, an annulus seal assembly must be installed between the casing hanger and the wellhead housing and then pressure tested to verify its integrity. Current methods for pressure testing annulus seal assemblies often require the use of a blowout preventer (BOP). The pressure test is performed by closing the BOP rams, pressurizing the space between the seal assembly and the BOP rams to the required test pressure and then holding the pressure for a specified period of time.
In order to use a BOP, however, a riser usually must also be used. A riser is an assembly of tubing which is connected between the BOP and a surface vessel. Since the surface vessel needs to maintain constant tension on the riser, the surface vessel must be rated for the combined weight of the riser and the BOP. However, at the great depths at which drilling is currently being conducted, a limited number of surface vessels exist which are rated for the weight of the necessary risers. Therefore, for projects which require such a riser, but for which an appropriate surface vessel is not available, no simple solutions exist for setting and pressure testing the annulus seal assembly.
Slim bore wellhead systems allow for the use of smaller diameter drilling risers and are therefore able to accommodate greater water depths for a given riser weight. In addition, these systems allow the annulus seal assembly to be set and pressure tested without a riser. However, two different running tools requiring two different trips from the surface vessel must be used to perform the setting and testing operations if a riser is not used, and in deep water locations it is desirable to reduce the number of trips into a well. Moreover, while slim bore wellhead systems provide a solution to the problem of water depth, they have certain disadvantages. Because slim bore wellheads are smaller in diameter than standard wellhead systems, the operator is limited in the number of total casing strings which can be used to reach a total depth below the sea floor. Therefore, many reservoirs which would be attainable using a large bore wellhead system cannot be reached with slim bore wellhead systems.